1. Technical Field
The present invention relates to a variable magnification optical system capable of maintaining the maximum aperture F-number bright from the wide angle end to the telephoto end, and an imaging apparatus which includes the variable magnification optical system.
2. Background Art
As zoom lenses (variable magnification optical systems) for use with CCTV (Closed-circuit Television) designed to meet the surveillance camera specifications that can be used both in visible region and near infrared region, and allow image capturing even at night as well as during the day, a plurality of four group zoom lenses having positive, negative, positive, and positive refractive powers has been proposed in the past (Japanese Unexamined Patent Publication No. 2011-118372, Japanese Unexamined Patent Publication No. 6(1994)-230317, Japanese Unexamined Patent Publication No. 2011-158630, and the like). The four group zoom lenses having positive, negative, positive, and positive refractive powers have many advantages, including ease of handling along with the simplicity of the lens barrel·magnification change mechanism and such configuration has conventionally been employed frequently.
Note that such zoom lenses may well be used for imaging devices, other than CCTV, such as video cameras, electronic still cameras, and the like, having image sensors, such as CCD (Charge Coupled Device), CMOS (Complementary Metal Oxide Semiconductor) and the like as recording media.